Which version of R is running in my computer?

Run R --version there's info about version on the first line.

Edit: If you ask this question then I bet that R is not running from any of these directories. Check $PATH env variable to get information where binaries are looked for and in which order.

Edit 2: Use type shell command to find where binary for given command is stored, -a for all paths, -f for the hashed one (basically: most recently used).